1. Field of the Invention
This invention relates to an epoxy resin composition, and more particularly it relates to an epoxy resin composition which is useful for preparing electrical insulating materials.
2. Description of the Prior Art
Thermosetting epoxy resins are well known and have been conventionally used as coating and molding compositions. The bisphenol A type epoxy resin compositions which contain an acid anhydride curing agent and an epoxy resin prepared by the condensation of bisphenol A and epichlorohydrin are especially useful as molding and casting compositions. In some applications, an alicyclic epoxy resin containing no aromatic ring has been used as well as an epoxy resin composition comprising a glycidyl ester and an acid anhydride curing agent.
When the cured product prepared from a bisphenol A type epoxy resin composition is used as an electric insulating material under a polluted condition, the cracking resistance (Arc resistance) of the cured product is inferior. Therefore, it is difficult to maintain the insulating property of the product for a long time.
A glycidyl ester type epoxy resin composition is usually used to cast large articles or to cast an article which fills a metal part. However, such compositions are easily cracked as a result of the rapid change in temperature to which these objects are often necessarily subjected. Also, their mechanical properties are inferior to those of the cured product prepared from a bisphenol A type epoxy resin composition.
As noted above, the conventional epoxy resin compositions have various disadvantages which make them unsatisfactory for use as an electrical insulating material under a polluted condition. Therefore, a need exists to obtain an epoxy resin composition for molding which has superior electric properties, especially excellent tracking resistance, mechanical properties and thermal resistance.